1. Field of the Invention
The present invention relates to an image forming method including the steps of developing an electrostatic latent image and transferring a toner image onto a belt transfer body.
2. Description of the Related Art
As conventional methods of visualizing an electrostatic latent image formed on a photoconductive photoreceptor or the like by using toner in the electrophotographic method, for example, a magnetic brush method described in U.S. Pat. No. 2,874,063, a cascade method described in U.S. Pat. No. 2,618,552, the powder cloud method described in U.S. Pat. No. 2,221,776, etc. have been known. Meanwhile, in cases where a multi-color image is obtained by the electronic needling method, a method in which colors are superposed successively for each color by repeating the charging, exposure, development and cleaning processes is used. In this method, a multi-color image is formed on a transfer drum having a drum shape, and thus the problem arose of the apparatus to house the drum. In order to solve this problem, making the image forming apparatus smaller has been attempted by using a flexible belt-shaped transfer body (hereinafter, referred to as "belt transfer body").
As a developer for developing an electrostatic latent image using the electrophotographic method, a two-component developer composed of a toner and a carrier is often used. Various carriers are used in the two-component developer, typical examples being an electroconductive carriers such as iron oxide powder, and coat-type insulating carriers. Further, a toner, which is obtained by mixing a coloring material with a thermoplastic resin is generally used. Furthermore, various organic and inorganic fine powders added as additives give process adaptability by improving flow, charge, and cleaning properties, and the like. Examples of powders proposed for this use include fine powders of silicon oxide (silica), titanium oxide, alumina, and tin oxide. In particular, titanium oxide fine powder has been frequently used in recent years because of its excellent environmental reliability, electric charge exchangeability, and flowability when added to the toner externally.
In recent years, longer life of the developer is desired. Therefore, in order to lower non-electrostatic adhesion between the toner and carrier, and prevent contamination of the carrier by the toner, it is suggested that the surface of the carrier be coated with a fluorine-containing resin so that the life of the developer may be lengthened.
Further, the need for high image quality has increased in recent years, and thus various improvements in image forming apparatuses and developers have been tried in order to satisfy such needs. An image forming apparatus includes development, transfer, cleaning, and fixing process, but particularly in the transfer process, an image is deteriorated remarkably, and in an image forming apparatus using a belt transfer body, a sufficiently high image quality has not been yet obtained. Moreover, when an image is copied on plural sheets of paper with a low image density, the developer deteriorates, and thus problems arise such as the transfer efficiency being lowered.